The natural maintenance cycle of LAC virus in forested areas will be studied in field and laboratory research focused on mechanisms and relative importance of vertical (transvarial) and horizontal (venereal and salivary transfer through mammals) transmission of virus. Data on isolates from the mosquito vector and antibody rates in chipmunks and squirrels obtained from studies in an endemic area in suburban La Crosse will be compared with those obtained from the edge of this endemic area in central Wisconsin and from islands of LAC activity as recently located in a highly-populated suburban area near Milwaukee in eastern Wisconsin. Selected cases of California encephalitis, occurring each year in Wisconsin and other midwestern states, will be studied for distribution and circumstances of infection. Results of epidemiologic surveys to be conducted in residents of the newly found isolated area of LAC virus in highly-populated eastern Wisconsin will be compared with results recently obtained in residents in the endemic area. Enhancement of venereal infection and transovarial and salivary transmission rates, so far observed with LAC virus in colonized female Aedes triseriatus given blood-meals before mating, will be further studied with naturally infected females and F1 progeny.